ABS Part Material for Electrophotography-Based Additive Manufacturing

ABSTRACT

A part material for printing three-dimensional parts with an electrophotography-based additive manufacturing system, the part material including a composition having a copolymer (including acrylonitrile units, butadiene units, and aromatic units), a charge control agent, and a heat absorber. The part material is provided in a powder form having a controlled particle size, and is configured for use in the electrophotography-based additive manufacturing system having a layer transfusion assembly for printing the three-dimensional parts in a layer-by-layer manner.

BACKGROUND

The present disclosure relates to additive manufacturing systems forprinting three-dimensional (3D) parts and support structures. Inparticular, the present disclosure relates to consumable materials forprinting 3D parts and support structures using an imaging process, suchas electrophotography.

Additive manufacturing systems are used to build 3D parts from digitalrepresentations of the 3D parts (e.g., AMF and STL format files) usingone or more additive manufacturing techniques. Examples of commerciallyavailable additive manufacturing techniques include extrusion-basedtechniques, ink jetting, selective laser sintering, powder/binderjetting, electron-beam melting, and stereolithographic processes. Foreach of these techniques, the digital representation of the 3D part isinitially sliced into multiple horizontal layers. For each sliced layer,a tool path is then generated, which provides instructions for theparticular additive manufacturing system to form the given layer.

For example, in an extrusion-based additive manufacturing system, a 3Dpart or model may be printed from a digital representation of the 3Dpart in a layer-by-layer manner by extruding a flowable part material.The part material is extruded through an extrusion tip carried by aprint head of the system, and is deposited as a sequence of roads on asubstrate in an x-y plane. The extruded part material fuses topreviously deposited part material, and solidifies upon a drop intemperature. The position of the print head relative to the substrate isthen incremented along a z-axis (perpendicular to the x-y plane), andthe process is then repeated to form a 3D part resembling the digitalrepresentation.

In fabricating 3D parts by depositing layers of a part material,supporting layers or structures are typically built underneathoverhanging portions or in cavities of objects under construction, whichare not supported by the part material itself. A support structure maybe built utilizing the same deposition techniques by which the partmaterial is deposited. The host computer generates additional geometryacting as a support structure for the overhanging or free-space segmentsof the 3D part being formed, and in some cases, for the sidewalls of the3D part being formed. The support material adheres to the part materialduring fabrication, and is removable from the completed 3D part when theprinting process is complete.

In two-dimensional (2D) printing, electrophotography (i.e., xerography)is a technology for creating 2D images on planar substrates, such asprinting paper and transparent substrates. Electrophotography systemstypically include a conductive support drum coated with aphotoconductive material layer, where latent electrostatic images areformed by electrostatic charging, followed by image-wise exposure of thephotoconductive layer by an optical source. The latent electrostaticimages are then moved to a developing station where toner is applied tocharged areas, or alternatively to discharged areas of thephotoconductive insulator to form visible images. The formed tonerimages are then transferred to substrates (e.g., printing paper) andaffixed to the substrates with heat and/or pressure.

SUMMARY

An aspect of the present disclosure is directed to a part material forprinting 3D parts with an electrophotography-based additivemanufacturing system. The part material has a composition that includesa copolymer comprising acrylonitrile units, butadiene units, andaromatic units, a charge control agent, and a heat absorber. The partmaterial is provided in a powder form having a controlled particle size(e.g., a D50 particle size ranging from about 5 micrometers to about 30micrometers), and is configured for use in the electrophotography-basedadditive manufacturing system having a layer transfusion assembly forprinting the 3D parts in a layer-by-layer manner.

Another aspect of the present disclosure is directed to a part materialfor printing 3D parts with an electrophotography-based additivemanufacturing system, where the part material has a composition thatincludes an acrylonitrile-butadiene-styrene (ABS) copolymer, a chargecontrol agent, a flow control agent, and a heat absorber. The partmaterial is provided in a powder form having a controlled particle sizeand an narrow particle size distribution, and is configured for use inthe electrophotography-based additive manufacturing system having alayer transfusion assembly for printing the three-dimensional parts in alayer-by-layer manner.

In some embodiments, the above-discussed part materials may be providedin interchangeable cartridges or other similar devices, along withcarrier particles, for use with the electrophotography-based additivemanufacturing systems.

Another aspect of the present disclosure is directed to a method forprinting a 3D part with an electrophotography-based additivemanufacturing system having an electrophotography engine, a transfermedium, and a layer transfusion assembly. The method includes providinga part material to the electrophotography-based additive manufacturingsystem, where the part material compositionally includes a chargecontrol agent, a heat absorber, and a copolymer having acrylonitrileunits, butadiene units, and aromatic units, and has a powder form.

The method also includes triboelectrically charging the part material toa desired triboelectric charge (e.g., a Q/M ratio having a negativecharge or a positive charge, and a magnitude ranging from about 5micro-Coulombs/gram to about 50 micro-Coulombs/gram), and developinglayers of the 3D part from the charged part material with theelectrophotography engine. The method further includes electrostaticallyattracting the developed layers from the electrophotography engine tothe transfer medium, moving the attracted layers to the layertransfusion assembly with the transfer medium, and transfusing the movedlayers to previously-printed layers of the 3D part with the layertransfusion assembly.

DEFINITIONS

Unless otherwise specified, the following terms as used herein have themeanings provided below:

The term “copolymer” refers to a polymer having two or more monomerspecies, and includes terpolymers (i.e., copolymers having three monomerspecies).

The terms “preferred” and “preferably” refer to embodiments of theinvention that may afford certain benefits, under certain circumstances.However, other embodiments may also be preferred, under the same orother circumstances. Furthermore, the recitation of one or morepreferred embodiments does not imply that other embodiments are notuseful, and is not intended to exclude other embodiments from theinventive scope of the present disclosure.

Reference to “a” chemical compound refers one or more molecules of thechemical compound, rather than being limited to a single molecule of thechemical compound. Furthermore, the one or more molecules may or may notbe identical, so long as they fall under the category of the chemicalcompound. Thus, for example, “an” ABS copolymer is interpreted toinclude one or more polymer molecules of the ABS copolymer, where thepolymer molecules may or may not be identical (e.g., different molecularweights and/or isomers).

The terms “at least one” and “one or more of” an element are usedinterchangeably, and have the same meaning that includes a singleelement and a plurality of the elements, and may also be represented bythe suffix “(s)” at the end of the element. For example, “at least oneABS copolymer”, “one or more ABS copolymers”, and “ABS copolymer(s)” maybe used interchangeably and have the same meaning.

Directional orientations such as “above”, “below”, “top”, “bottom”, andthe like are made with reference to a direction along a printing axis ofa 3D part. In the embodiments in which the printing axis is a verticalz-axis, the layer-printing direction is the upward direction along thevertical z-axis. In these embodiments, the terms “above”, “below”,“top”, “bottom”, and the like are based on the vertical z-axis. However,in embodiments in which the layers of 3D parts are printed along adifferent axis, the terms “above”, “below”, “top”, “bottom”, and thelike are relative to the given axis.

The term “providing”, such as for “providing a material” and the like,when recited in the claims, is not intended to require any particulardelivery or receipt of the provided item. Rather, the term “providing”is merely used to recite items that will be referred to in subsequentelements of the claim(s), for purposes of clarity and ease ofreadability.

Unless otherwise specified, temperatures referred to herein are based onatmospheric pressure (i.e. one atmosphere).

The terms “about” and “substantially” are used herein with respect tomeasurable values and ranges due to expected variations known to thoseskilled in the art (e.g., limitations and variabilities inmeasurements).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of an example electrophotography-based additivemanufacturing system for printing 3D parts and support structures frompart and support materials of the present disclosure.

FIG. 2 is a schematic front view of a pair of electrophotography enginesof the system for developing layers of the part and support materials.

FIG. 3 is a schematic front view of an alternative electrophotographyengine, which includes an intermediary drum or belt.

FIG. 4 is a schematic front view of a layer transfusion assembly of thesystem for performing layer transfusion steps with the developed layers.

FIG. 5 is a plot of dynamic viscosity versus temperature for examplepart materials of the present disclosure, illustrating melt rheologybehaviors of the part materials.

DETAILED DESCRIPTION

The present disclosure is directed to consumable materials, such as partand support materials, which are engineered for use in anelectrophotography-based additive manufacturing system to print 3D partsand support structures with high resolutions and fast printing rates.During a printing operation, electrophotography (EP) engines may developor otherwise image each layer of the part and support materials usingthe electrophotographic process. The developed layers are thentransferred to a layer transfusion assembly where they are transfused(e.g., using heat and/or pressure) to print one or more 3D parts andsupport structures in a layer-by-layer manner.

In comparison to 2D printing, in which developed toner particles can beelectrostatically transferred to printing paper by placing an electricalpotential through the printing paper, the multiple printed layers in a3D environment effectively prevents the electrostatic transfer of partand support materials after a given number of layers are printed (e.g.,about 15 layers). Instead, each layer may be heated to an elevatedtransfer temperature, and then pressed against a previously-printedlayer (or to a build platform) to transfuse the layers together in atransfusion step. This allows numerous layers of 3D parts and supportstructures to be built vertically, beyond what is otherwise achievablevia electrostatic transfers.

As discussed below, the part material is a powder-based,acrylonitrile-butadiene-styrene (ABS) part material that may be producedwith a limited coalescence process. The ABS part material includes anABS copolymer, a charge control agent (e.g., an internal triboelectriccharge control agent), preferably a heat absorber (e.g., an infraredabsorber), and optionally one or more additional materials, such as aflow control agent, which may also function as an externalsurface-treatment triboelectric charge control agent and/or atriboelectric modification additive. The ABS part material is engineeredfor use with electrophotography-based additive manufacturing systems toprint 3D parts having high part resolutions and good physical properties(e.g., good part strength, density, chemical resistance, usabletemperature ranges, and the like). This allows the resulting 3D parts tofunction as end-use parts, if desired.

FIGS. 1-4 illustrate system 10, which is an exampleelectrophotography-based additive manufacturing system for printing 3Dparts from the ABS part material of the present disclosure, andassociated support structures from a sacrificial support material. Asdiscussed further below, an example of a preferred support material foruse with the ABS part material includes a soluble support material asdisclosed in co-filed U.S. patent application Ser. No. ______, entitled“Soluble Support Material For Electrophotography-Based AdditiveManufacturing” (attorney docket no. S697.12-0261).

As shown in FIG. 1, system 10 includes a pair of EP engines 12 p and 12s, belt transfer assembly 14, biasing mechanisms 16 and 18, and layertransfusion assembly 20. Examples of suitable components and functionaloperations for system 10 include those disclosed in Hanson et al., U.S.Publication Nos. 2013/0077996 and 2013/0077997, and in Comb et al., U.S.patent application Ser. Nos. 13/790,382 and 13/790,406.

EP engines 12 p and 12 s are imaging engines for respectively imaging orotherwise developing layers of the part and support materials, where thepart and support materials are each preferably engineered for use withthe particular architecture of EP engine 12 p or 12 s. As discussedbelow, the imaged layers may then be transferred to belt transferassembly 14 (or other transfer medium) with biasing mechanisms 16 and18, and carried to layer transfusion assembly 20 to print the 3D partsand associated support structures in a layer-by-layer manner.

In the shown embodiment, belt transfer assembly 14 includes transferbelt 22, belt drive mechanisms 24, belt drag mechanisms 26, loop limitsensors 28, idler rollers 30, and belt cleaner 32, which are configuredto maintain tension on belt 22 while belt 22 rotates in the rotationaldirection of arrows 34. In particular, belt drive mechanisms 24 engageand drive belt 22, and belt drag mechanisms 26 may function as brakes toprovide a service loop design for protecting belt 22 against tensionstress, based on monitored readings via loop limit sensors 28.

System 10 also includes controller 36, which is one or more controlcircuits, microprocessor-based engine control systems, and/ordigitally-controlled raster imaging processor systems, and which isconfigured to operate the components of system 10 in a synchronizedmanner based on printing instructions received from host computer 38.Host computer 38 is one or more computer-based systems configured tocommunicate with controller 36 to provide the print instructions (andother operating information). For example, host computer 38 may transferinformation to controller 36 that relates to the sliced layers of the 3Dparts and support structures, thereby allowing system 10 to print the 3Dparts and support structures in a layer-by-layer manner.

The components of system 10 may be retained by one or more framestructures, such as frame 40. Additionally, the components of system 10are preferably retained within an enclosable housing (not shown) thatprevents ambient light from being transmitted to the components ofsystem 10 during operation.

FIG. 2 illustrates EP engines 12 p and 12 s, where EP engine 12 s (i.e.,the upstream EP engine relative to the rotational direction of belt 22)develops layers of the support material, and EP engine 12 p (i.e., thedownstream EP engine relative to the rotational direction of belt 22)develops layers of the part material. In alternative embodiments, thearrangement of EP engines 12 p and 12 s may be reversed such that EPengine 12 p is upstream from EP engine 12 s relative to the rotationaldirection of belt 22. In further alternative embodiments, system 10 mayinclude three or more EP engines for printing layers of additionalmaterials.

In the shown embodiment, EP engines 12 p and 12 s may include the samecomponents, such as photoconductor drum 42 having conductive drum body44 and photoconductive surface 46. Conductive drum body 44 is anelectrically-conductive drum (e.g., fabricated from copper, aluminum,tin, or the like) that is electrically grounded and configured to rotatearound shaft 48. Shaft 48 is correspondingly connected to drive motor50, which is configured to rotate shaft 48 (and photoconductor drum 42)in the direction of arrow 52 at a constant rate.

Photoconductive surface 46 is a thin film extending around thecircumferential surface of conductive drum body 44, and is preferablyderived from one or more photoconductive materials, such as amorphoussilicon, selenium, zinc oxide, organic materials, and the like. Asdiscussed below, surface 46 is configured to receive latent-chargedimages of the sliced layers of a 3D part or support structure (ornegative images), and to attract charged particles of the part orsupport material of the present disclosure to the charged or dischargedimage areas, thereby creating the layers of the 3D part or supportstructure.

As further shown, EP engines 12 p and 12 s also includes charge inducer54, imager 56, development station 58, cleaning station 60, anddischarge device 62, each of which may be in signal communication withcontroller 36. Charge inducer 54, imager 56, development station 58,cleaning station 60, and discharge device 62 accordingly define animage-forming assembly for surface 46 while drive motor 50 and shaft 48rotate photoconductor drum 42 in the direction of arrow 52.

In the shown example, the image-forming assembly for surface 46 of EPengine 12 s is used to form layers 64 s of the support material(referred to as support material 66 s), where a supply of supportmaterial 66 s may be retained by development station 58 (of EP engine 12s) along with carrier particles. Similarly, the image-forming assemblyfor surface 46 of EP engine 12 p is used to form layers 64 p of the partmaterial (referred to as part material 66 p), where a supply of partmaterial 66 p may be retained by development station 58 (of EP engine 12p) along with carrier particles.

Charge inducer 54 is configured to generate a uniform electrostaticcharge on surface 46 as surface 46 rotates in the direction of arrow 52past charge inducer 54. Suitable devices for charge inducer 54 includecorotrons, scorotrons, charging rollers, and other electrostaticcharging devices.

Imager 56 is a digitally-controlled, pixel-wise light exposure apparatusconfigured to selectively emit electromagnetic radiation toward theuniform electrostatic charge on surface 46 as surface 46 rotates in thedirection of arrow 52 past imager 56. The selective exposure of theelectromagnetic radiation to surface 46 is directed by controller 36,and causes discrete pixel-wise locations of the electrostatic charge tobe removed (i.e., discharged to ground), thereby forming latent imagecharge patterns on surface 46.

Suitable devices for imager 56 include scanning laser (e.g., gas orsolid state lasers) light sources, light emitting diode (LED) arrayexposure devices, and other exposure device conventionally used in 2Delectrophotography systems. In alternative embodiments, suitable devicesfor charge inducer 54 and imager 56 include ion-deposition systemsconfigured to selectively directly deposit charged ions or electrons tosurface 46 to form the latent image charge pattern. As such, as usedherein, the term “electrophotography” includes ionography.

Each development station 58 is an electrostatic and magnetic developmentstation or cartridge that retains the supply of part material 66 p orsupport material 66 s, preferably in powder form, along with carrierparticles. Development stations 58 may function in a similar manner tosingle or dual component development systems and toner cartridges usedin 2D electrophotography systems. For example, each development station58 may include an enclosure for retaining the part material 66 p orsupport material 66 s and carrier particles. When agitated, the carrierparticles generate triboelectric charges to attract the powders of thepart material 66 p or support material 66 s, which charges the attractedpowders to a desired sign and magnitude, as discussed below.

Each development station 58 may also include one or more devices fortransferring the charged part material 66 p or support material 66 s tosurface 46, such as conveyors, fur brushes, paddle wheels, rollers,and/or magnetic brushes. For instance, as surface 46 (containing thelatent charged image) rotates from imager 56 to development station 58in the direction of arrow 52, the charged part material 66 p or supportmaterial 66 s is attracted to the appropriately charged regions of thelatent image on surface 46, utilizing either charged area development ordischarged area development (depending on the electrophotography modebeing utilized). This creates successive layers 64 p or 64 s asphotoconductor drum 12 continues to rotate in the direction of arrow 52,where the successive layers 64 p or 64 s correspond to the successivesliced layers of the digital representation of the 3D part or supportstructure.

The successive layers 64 p or 64 s are then rotated with surface 46 inthe direction of arrow 52 to a transfer region in which layers 64 p or64 s are successively transferred from photoconductor drum 42 to belt22, as discussed below. While illustrated as a direct engagement betweenphotoconductor drum 42 and belt 22, in some preferred embodiments, EPengines 12 p and 12 s may also include intermediary transfer drumsand/or belts, as discussed further below.

After a given layer 64 p or 64 s is transferred from photoconductor drum42 to belt 22 (or an intermediary transfer drum or belt), drive motor 50and shaft 48 continue to rotate photoconductor drum 42 in the directionof arrow 52 such that the region of surface 46 that previously held thelayer 64 p or 64 s passes cleaning station 60. Cleaning station 60 is astation configured to remove any residual, non-transferred portions ofpart or support material 66 p or 66 s. Suitable devices for cleaningstation 60 include blade cleaners, brush cleaners, electrostaticcleaners, vacuum-based cleaners, and combinations thereof.

After passing cleaning station 60, surface 46 continues to rotate in thedirection of arrow 52 such that the cleaned regions of surface 46 passdischarge device 62 to remove any residual electrostatic charge onsurface 46, prior to starting the next cycle. Suitable devices fordischarge device 62 include optical systems, high-voltagealternating-current corotrons and/or scorotrons, one or more rotatingdielectric rollers having conductive cores with applied high-voltagealternating-current, and combinations thereof.

Transfer belt 22 is a transfer medium for transferring the developedsuccessive layers 64 p and 64 s from photoconductor drum 42 (or anintermediary transfer drum or belt) to layer transfusion assembly 16.Examples of suitable transfer belts for belt 22 include those disclosedin Comb et al., U.S. patent application Ser. Nos. 13/790,382 and13/790,406. Belt 22 includes front surface 22 a and rear surface 22 b,where front surface 22 a faces surface 46 of photoconductor drums 42 andrear surface 22 b is in contact with biasing mechanisms 16 and 18.

Biasing mechanisms 16 and 18 are configured to induce electricalpotentials through belt 22 to electrostatically attract layers 64 p and64 s from EP engines 12 p and 12 s to belt 22. Because layers 64 p and64 s are each only a single layer increment in thickness at this pointin the process, electrostatic attraction is suitable for transferringlayers 64 p and 64 s from EP engines 12 p and 12 s to belt 22.

Controller 36 preferably rotates photoconductor drums 36 of EP engines12 p and 12 s at the same rotational rates that are synchronized withthe line speed of belt 22 and/or with any intermediary transfer drums orbelts. This allows system 10 to develop and transfer layers 64 p and 66s in coordination with each other from separate developer images. Inparticular, as shown, each part layer 64 p may be transferred to belt 22with proper registration with each support layer 64 s to preferablyproduce a combined part and support material layer 64. This allowslayers 64 p and 64 s to be transfused together, requiring the part andsupport materials to have thermal properties and melt rheologies thatare similar or substantially the same. As can be appreciated, somelayers transferred to layer transfusion assembly 20 may only includesupport material 66 s or may only include part material 66 p, dependingon the particular support structure and 3D part geometries and layerslicing.

In an alternative and less-preferred embodiment, part layers 64 p andsupport layers 64 s may optionally be developed and transferred alongbelt 22 separately, such as with alternating layers 64 p and 64 s. Thesesuccessive, alternating layers 64 p and 64 s may then be transferred tolayer transfusion assembly 20, where they may be transfused separatelyto print the 3D part and support structure.

In some preferred embodiments, one or both of EP engines 12 p and 12 smay also include one or more intermediary transfer drums and/or beltsbetween photoconductor drum 42 and belt 22. For example, as shown inFIG. 3, EP engine 12 p may also include intermediary drum 42 a thatrotates an opposing rotational direction from arrow 52, as illustratedby arrow 52 a, under the rotational power of motor 50 a. Intermediarydrum 42 a engages with photoconductor drum 42 to receive the developedlayers 64 p from photoconductor drum 42, and then carries the receiveddeveloped layers 64 p and transfers them to belt 22.

EP engine 12 s may include the same arrangement of intermediary drum 42a for carrying the developed layers 64 s from photoconductor drum 42 tobelt 22. The use of such intermediary transfer drums or belts for EPengines 12 p and 12 s can be beneficial for thermally isolatingphotoconductor drum 42 from belt 22, if desired.

FIG. 4 illustrates an example embodiment for layer transfusion assembly20. As shown, layer transfusion assembly 20 includes build platform 68,nip roller 70, heaters 72 and 74, post-fuse heater 76, and air jets 78(or other cooling units). Build platform 68 is a platform assembly orplaten of system 10 that is configured to receive the heated combinedlayers 64 (or separate layers 64 p and 64 s) for printing a 3D part andsupport structure, referred to as 3D part 80 and support structure 82,in a layer-by-layer manner. In some embodiments, build platform 68 mayinclude removable film substrates (not shown) for receiving the printedlayers 64, where the removable film substrates may be restrained againstbuild platform using any suitable technique (e.g., vacuum drawing,removable adhesive, mechanical fastener, and the like).

Build platform 68 is supported by gantry 84, which is a gantry mechanismconfigured to move build platform 68 along the z-axis and the x-axis toproduce a reciprocating rectangular pattern, where the primary motion isback-and-forth along the x-axis (illustrated by broken lines 86. Gantry84 may be operated by motor 88 based on commands from controller 36,where motor 88 may be an electrical motor, a hydraulic system, apneumatic system, or the like.

In the shown embodiment, build platform 68 is heatable with heatingelement 90 (e.g., an electric heater). Heating element 90 is configuredto heat and maintain build platform 68 at an elevated temperature thatis greater than room temperature (25° C.), such as at a desired averagepart temperature of 3D part 80 and/or support structure 82, as discussedin Comb et al., U.S. patent application Ser. Nos. 13/790,382 and13/790,406. This allows build platform 68 to assist in maintaining 3Dpart 80 and/or support structure 82 at this average part temperature.

Nip roller 70 is an example heatable element or heatable layertransfusion element, which is configured to rotate around a fixed axiswith the movement of belt 22. In particular, nip roller 70 may rollagainst rear surface 22 b in the direction of arrow 92 while belt 22rotates in the direction of arrow 34. In the shown embodiment, niproller 70 is heatable with heating element 94 (e.g., an electricheater). Heating element 94 is configured to heat and maintain niproller 70 at an elevated temperature that is greater than roomtemperature (25° C.), such as at a desired transfer temperature forlayers 64.

Heater 72 is one or more heating devices (e.g., an infrared heaterand/or a heated air jet) configured to heat layers 64 to a temperaturenear an intended transfer temperature of the part and support materials,such as at least a fusion temperature of the part and support materials,preferably prior to reaching nip roller 70. Each layer 64 desirablypasses by (or through) heater 72 for a sufficient residence time to heatthe layer 64 to the intended transfer temperature. Heater 74 mayfunction in the same manner as heater 72, and heats the top surfaces of3D part 80 and support structure 82 to an elevated temperature, such asat the same transfer temperature as the heated layers 64 (or othersuitable elevated temperature).

As mentioned above, the support material 66 s used to print supportstructure 82 preferably has thermal properties (e.g., glass transitiontemperature) and a melt rheology that are similar to or substantiallythe same as the thermal properties and the melt rheology of the partmaterial 66 p used to print 3D part 80. This allows part and supportmaterials of layers 64 p and 64 s to be heated together with heater 74to substantially the same transfer temperature, and also allows the partand support materials at the top surfaces of 3D part 80 and supportstructure 82 to be heated together with heater 74 to substantially thesame temperature. Thus, the part layers 64 p and the support layers 64 smay be transfused together to the top surfaces of 3D part 80 and supportstructure 82 in a single transfusion step as combined layer 64. Thissingle transfusion step for transfusing the combined layer 64 is notbelieved to be feasible without matching the thermal properties and themelt rheologies of the part and support materials.

Post-fuse heater 76 is located downstream from nip roller 70 andupstream from air jets 78, and is configured to heat the transfusedlayers to an elevated temperature in the post-fuse or heat-setting step.Again, the similar thermal properties and melt rheologies of the partand support materials allow post-fuse heater 76 to post-heat the topsurfaces of 3D part 80 and support structure 82 together in a singlepost-fuse step.

Prior to printing 3D part 80 and support structure 82, build platform 68and nip roller 70 may be heated to their desired temperatures. Forexample, build platform 68 may be heated to the average part temperatureof 3D part 80 and support structure 82 (due to the close melt rheologiesof the part and support materials). In comparison, nip roller 70 may beheated to a desired transfer temperature for layers 64 (also due to thesimilar thermal properties and melt rheologies of the part and supportmaterials).

During the printing operation, belt 22 carries a layer 64 past heater72, which may heat the layer 64 and the associated region of belt 22 tothe transfer temperature. Suitable transfer temperatures for the partand support materials include temperatures that exceed the glasstransition temperatures of the part and support materials, which arepreferably similar or substantially the same, and where the part andsupport materials of layer 64 are softened but not melted (e.g., atemperature of ranging from about 140° C. to about 180° C. for the ABSpart material).

As further shown in FIG. 4, during operation, gantry 84 may move buildplatform 68 (with 3D part 80 and support structure 82) in areciprocating rectangular pattern 86. In particular, gantry 84 may movebuild platform 68 along the x-axis below, along, or through heater 74.Heater 74 heats the top surfaces of 3D part 80 and support structure 82to an elevated temperature, such as the transfer temperatures of thepart and support materials. As discussed in Comb et al., U.S. patentapplication Ser. Nos. 13/790,382 and 13/790,406, heaters 72 and 74 mayheat layers 64 and the top surfaces of 3D part 80 and support structure82 to about the same temperatures to provide a consistent transfusioninterface temperature. Alternatively, heaters 72 and 74 may heat layers64 and the top surfaces of 3D part 80 and support structure 82 todifferent temperatures to attain a desired transfusion interfacetemperature.

The continued rotation of belt 22 and the movement of build platform 68align the heated layer 64 with the heated top surfaces of 3D part 80 andsupport structure 82 with proper registration along the x-axis. Gantry84 may continue to move build platform 68 along the x-axis, at a ratethat is synchronized with the rotational rate of belt 22 in thedirection of arrow 34 (i.e., the same directions and speed). This causesrear surface 22 b of belt 22 to rotate around nip roller 70 to nip belt22 and the heated layer 64 against the top surfaces of 3D part 80 andsupport structure 82. This presses the heated layer 64 between theheated top surfaces of 3D part 80 and support structure 82 at thelocation of nip roller 70, which at least partially transfuses heatedlayer 64 to the top layers of 3D part 80 and support structure 82.

As the transfused layer 64 passes the nip of nip roller 70, belt 22wraps around nip roller 70 to separate and disengage from build platform68. This assists in releasing the transfused layer 64 from belt 22,allowing the transfused layer 64 to remain adhered to 3D part 80 andsupport structure 82. Maintaining the transfusion interface temperatureat a transfer temperature that is higher than the glass transitiontemperatures of the part and support materials, but lower than theirfusion temperatures, allows the heated layer 64 to be hot enough toadhere to 3D part 80 and support structure 82, while also being coolenough to readily release from belt 22. Additionally, as discussedabove, the similar thermal properties and melt rheologies of the partand support materials allow them to be transfused in the same step.

After release, gantry 84 continues to move build platform 68 along thex-axis to post-fuse heater 76. At post-fuse heater 76, the top-mostlayers of 3D part 80 and support structure 82 (including the transfusedlayer 64) may then be heated to at least the fusion temperature of thepart and support materials in a post-fuse or heat-setting step. Thismelts the part and support materials of the transfused layer 64 to ahighly fusable state such that polymer molecules of the transfused layer64 quickly interdiffuse to achieve a high level of interfacialentanglement with 3D part 80 and support structure 82.

Additionally, as gantry 84 continues to move build platform 68 along thex-axis past post-fuse heater 76 to air jets 78, air jets 78 blow coolingair towards the top layers of 3D part 80 and support structure 82. Thisactively cools the transfused layer 64 down to the average parttemperature, as discussed in Comb et al., U.S. patent application Ser.Nos. 13/790,382 and 13/790,406.

To assist in keeping 3D part 80 and support structure 82 at the averagepart temperature, in some preferred embodiments, heater 74 and/orpost-heater 76 may operate to heat only the top-most layers of 3D part80 and support structure 82. For example, in embodiments in whichheaters 72, 74, and 76 are configured to emit infrared radiation, 3Dpart 80 and support structure 82 may include heat absorbers and/or othercolorants configured to restrict penetration of the infrared wavelengthsto within the top-most layers. Alternatively, heaters 72, 74, and 76 maybe configured to blow heated air across the top surfaces of 3D part 80and support structure 82. In either case, limiting the thermalpenetration into 3D part 80 and support structure 82 allows the top-mostlayers to be sufficiently transfused, while also reducing the amount ofcooling required to keep 3D part 80 and support structure 82 at theaverage part temperature.

Gantry 84 may then actuate build platform 68 downward, and move buildplatform 68 back along the x-axis to a starting position along thex-axis, following the reciprocating rectangular pattern 86. Buildplatform 68 desirably reaches the starting position for properregistration with the next layer 64. In some embodiments, gantry 84 mayalso actuate build platform 68 and 3D part 80/support structure 82upward for proper registration with the next layer 64. The same processmay then be repeated for each remaining layer 64 of 3D part 80 andsupport structure 82.

In some preferred embodiments, a resulting 3D part 80 is encasedlaterally (i.e., horizontally to the build plane) in the supportstructure 82, such as shown in FIG. 4. This is believed to provide gooddimensional integrity and surface quality for the 3D part 80 while usinga reciprocating build platen 68 and a nip roller 70.

After the printing operation is completed, the resulting 3D part 80 andsupport structure 82 may be removed from system 10 and undergo one ormore post-printing operations. For example, support structure 82 derivedfrom the support material of the present disclosure may be sacrificiallyremoved from 3D part 80, such as by using an aqueous-based solution(e.g., an aqueous alkali solution). For instance, an example of apreferred support material for use with the ABS part material includes asoluble support material as disclosed in co-filed U.S. patentapplication Ser. No. ______, entitled “Soluble Support Material ForElectrophotography-Based Additive Manufacturing” (attorney docket no.S697.12-0261). Under this preferred soluble technique, support structure82 may at least partially dissolve in the solution, separating it from3D part 80 in a hands-free manner.

In comparison, part materials such as the ABS part material arechemically resistant to aqueous alkali solutions. This allows the use ofan aqueous alkali solution to be employed for removing the sacrificialsupport structure 82 without degrading the shape or quality of 3D part80. Examples of suitable systems and techniques for removing supportstructure 82 in this manner include those disclosed in Swanson et al.,U.S. Pat. No. 8,459,280; Hopkins et al., U.S. Pat. No. 8,246,888; andDunn et al., U.S. Publication No. 2011/0186081; each of which areincorporated by reference to the extent that they do not conflict withthe present disclosure.

Furthermore, after support structure 82 is removed, 3D part 80 mayundergo one or more additional post-printing processes, such as surfacetreatment processes. Examples of suitable surface treatment processesinclude those disclosed in Priedeman et al., U.S. Pat. No. 8,123,999;and in Zinniel, U.S. Publication No. 2008/0169585.

As briefly discussed above, the part material of the present disclosure,referred to herein as the “ABS part material”, compositionally includesan acrylonitrile-butadiene-styrene (ABS) copolymer, a charge controlagent, preferably a heat absorber (e.g., an infrared absorber), andoptionally one or more additional materials, such as a flow controlagent. As mentioned above, the ABS part material is preferablyengineered for use with the particular architecture of EP engine 12 p.

The ABS copolymer is polymerized from monomers that preferably includeacrylonitrile, butadiene, and an aromatic monomer such as styrene.Example acrylonitrile monomers have the following structure:

N≡C—CH═CH₂  (Formula 1)

where, in some embodiments, the hydrogen atoms in Formula 1 may beindependently substituted with one or more optional low-atomic weightgroups, such as an alkyl or ether group having 1-3 carbon atoms.Furthermore, in some embodiments, the ethylenically-unsaturated groupand the cyano group may be separated by an optional chain linkage, suchas a hydrocarbon or ether linkage having 1-8 carbon atoms. Morepreferably, the acrylonitrile monomer includes the structure shown abovein Formula 1, with the ethylenically-unsaturated vinyl group extendingdirectly from the cyano group.

Example butadiene monomers have the following structure:

H₂C═CH—CH═CH₂  (Formula 2)

where, in some embodiments, the hydrogen atoms in Formula 2 may beindependently substituted with one or more optional low-atomic weightgroups, such as an alkyl or ether group having 1-3 carbon atoms.Furthermore, in some embodiments, the pair of ethylenically-unsaturatedgroups may be separated by an optional chain linkage, such as ahydrocarbon or ether linkage having 1-8 carbon atoms. More preferably,the butadiene monomer includes the structure shown above in Formula 2,with the pair of ethylenically-unsaturated vinyl groups extendingdirectly from each other.

Example aromatic monomers have the following structure:

where, in some embodiments, the hydrogen atoms in Formula 3 may beindependently substituted with one or more optional low-atomic weightgroups, such as an alkyl or ether group having 1-3 carbon atoms.Furthermore, in some embodiments, the ethylenically-unsaturated groupand the aromatic group may be separated by an optional chain linkage,such as a hydrocarbon or ether linkage having 1-8 carbon atoms. In somefurther embodiments, one or more hydrogen atoms of the aromatic groupmay be independently substituted with one or more optional low-atomicweight groups, such as an alkyl or ether group having 1-3 carbon atoms.More preferably, the aromatic monomer includes the structure shown abovein Formula 3, with the ethylenically-unsaturated vinyl group extendingdirectly from the aromatic group (i.e., styrene).

The monomers may be polymerized with a free-radical polymerizationreaction using any suitable free-radical initiator. For example, atleast a portion of the butadiene monomers may be initially polymerizedto produce polybutadiene. Then the acrylonitrile and aromatic monomersmay then be polymerized in the presence of the polybutadiene to producelong polybutadiene chains that are linked with shorter chains from theacrylonitrile and aromatic monomers (e.g., poly(styrene-acrylonitrile)chains). The nitrile groups of neighboring chains are believed toattract and bind the chains together, providing good strengths for theresulting ABS copolymer. The ABS copolymer may exist as an amorphoustwo-phase system having a continuous phase of the polymerizedacrylonitrile and the aromatic monomers, and a dispersed phase of thepolybutadiene that is dispersed or otherwise distributed in thecontinuous phase.

The acrylonitrile monomers used to produce the ABS copolymer mayconstitute from about 10% to about 45% by weight, and more preferablyfrom about 15% to about 35% by weight, based on an entire weight ofmonomers used to produce the ABS copolymer. The butadiene monomers mayconstitute from about 1% to about 50% by weight, and more preferablyfrom about 5% to about 35% by weight, based on the entire weight of themonomers used to produce the ABS copolymer. Similarly, the aromaticmonomers (e.g., styrene) may constitute from about 30% to about 75% byweight, and more preferably from about 40% to about 60% by weight, basedon the entire weight of the monomers used to produce the ABS copolymer.

In some embodiments, the monomers used to polymerize the ABS copolymermay include one or more additional monomer compounds that preferably donot significantly detract from the strength, chemical, or thermalproperties of the ABS copolymer. For example, the ABS copolymer mayinclude monomers that function as chain extending units (e.g., ethyleneunits) for the polybutadiene backbone and/or thepoly(styrene-acrylonitrile) chains.

Accordingly, the additional monomers may collectively constitute from 0%by weight to about 10% by weight, based on the entire weight of themonomers used to produce the ABS copolymer. In some embodiment, theadditional monomers may from about 0.1% to about 5% by weight, based onthe entire weight of the monomers used to produce the ABS copolymer. Theremainder of the monomers used to polymerize the ABS copolymeraccordingly consist of the above-discussed acrylonitrile monomers, thebutadiene monomers, and the aromatic monomers (e.g., styrene)

In other preferred embodiments, the monomers used to polymerize the ABScopolymer consist essentially or completely of the acrylonitrilemonomers, the butadiene monomers, and the aromatic monomers (e.g.,styrene). In more preferred embodiments, the monomers used to polymerizethe ABS copolymer consist essentially or completely of the monomershaving structures as shown above in Formulas 1-3.

Additionally, in some embodiments, modifications can be made whenproducing the ABS copolymer in order to modify the impact resistance,toughness, and/or heat resistance. For example, impact resistance can beincreased by increasing the proportion of the butadiene monomersrelative to the acrylonitrile and aromatic monomers.

The ABS copolymer preferably has a molecular weight that providessuitable melt rheologies for use in an EP-based additive manufacturingsystem (e.g., system 10) to print 3D parts (e.g., 3D part 80), which maybe characterized by the glass transition temperature, melt flow rate,and/or dynamic viscosity of the ABS copolymer. Examples of preferredglass transition temperatures for the ABS copolymer range from about100° C. to about 115° C., more preferably from about 105° C. to about110° C.

Suitable dynamic viscosities for the ABS copolymer at 180° C. range fromabout 17 kilopascal-seconds to about 24 kilopascal-seconds, at 190° C.range from about 6 kilopascal-seconds to about 10 kilopascal-seconds,and at 200° C. range from about 3.5 kilopascal-seconds to about 4.5kilopascal-seconds. The dynamic viscosities referred to herein aredetermined pursuant to the Melt Rheology test described below.

As mentioned above, the ABS part material is engineered for use in anEP-based additive manufacturing system (e.g., system 10) to print 3Dparts (e.g., 3D part 80). As such, the ABS part material may alsoinclude one or more materials to assist in developing layers with EPengine 12 p, to assist in transferring the developed layers from EPengine 12 p to layer transfusion assembly 20, and to assist intransfusing the developed layers with layer transfusion assembly 20.

For example, in the electrophotographic process with system 10, the ABSpart material is preferably charged triboelectrically through themechanism of frictional contact charging with carrier particles atdevelopment station 58. This charging of the ABS part material may bereferred to by its triboelectric charge-to-mass (Q/M) ratio, which maybe a positive or negative charge and has a desired magnitude. The Q/Mratio is inversely proportional to the powder density of the ABS partmaterial, which can be referred to by its mass per unit area (M/A)value. For a given applied development field, as the value of Q/M ratioof the ABS part material is increased from a given value, the M/A valueof the ABS part material decreases, and vice versa. Thus, the powderdensity for each developed layer of the part material is a function ofthe Q/M ratio of the ABS part material.

It has been found that, in order to provide successful and reliabledevelopment of the ABS part material onto development drum 44 andtransfer to layer transfusion assembly 20 (e.g., via belt 22), and toprint 3D part 80 with a good material density, the ABS part materialpreferably has a suitable Q/M ratio for the particular architecture ofEP engine 12 p and belt 22. Examples of preferred Q/M ratios for the ABSpart material range from about −5 micro-Coulombs/gram (μC/g) to about−50 μC/g, more preferably from about −10 μC/g to about −40 μC/g, andeven more preferably from about −15 μC/g to about −35 μC/g, and evenmore preferably from about −25 μC/g to about −30 μC/g.

In this embodiment, the Q/M ratio is based on a negative triboelectriccharge. However, in an alternative embodiment, system 10 may operatesuch that the Q/M ratio of the ABS part material has a positivetriboelectric charge with the above-discussed magnitudes. In eitherembodiment, these magnitudes of Q/M ratio prevent the electrostaticforces constraining the ABS part material to the carrier surfaces frombeing too excessive, and that any level of “wrong sign” powder isminimized. This reduces inefficiencies in the development of the ABSpart material at EP engine 12 p, and facilitates the development andtransfer of each layer 64 p with the desired M/A value.

Furthermore, if a consistent material density of 3D part 80 is desired,the desired Q/M ratio (and corresponding M/A value) is preferablymaintained at a stable level during an entire printing operation withsystem 10. However, over extended printing operations with system 10,development station 58 of EP engine 12 p may need to be replenished withadditional amounts of the ABS part material. This can present an issuebecause, when introducing additional amounts of the ABS part material todevelopment station 58 for replenishment purposes, the ABS part materialis initially in an uncharged state until mixing with the carrierparticles. As such, the ABS part material also preferably charges to thedesired Q/M ratio at a rapid rate to maintain a continuous printingoperation with system 10.

Accordingly, controlling and maintaining the Q/M ratio during initiationof the printing operation, and throughout the duration of the printingoperation, will control the resultant rate and consistency of the M/Avalue of the ABS part material. In order to reproducibly and stablyachieve the desired Q/M ratio, and hence the desired M/A value, overextended printing operations, the ABS part material preferably includesone or more charge control agents, which may be added to the ABScopolymer during the manufacturing process of the ABS part material.

In embodiments in which the Q/M ratio of the ABS part material has anegative charge, suitable charge control agents for use in the ABS partmaterial include acid metal complexes (e.g., oxy carboxylic acidcomplexes of chromium, zinc, and aluminum), azo metal complexes (e.g.,chromium azo complexes and iron azo complexes), mixtures thereof, andthe like.

Alternatively, in embodiments in which the Q/M ratio of the ABS partmaterial has a positive charge, suitable charge control agents for usein the ABS part material include azine-based compounds, and quaternaryammonium salts, mixtures thereof, and the like. These agents areeffective at positively charging the ABS copolymer when frictionallycontact charged against appropriate carrier particles.

The charge control agents preferably constitute from about 0.1% byweight to about 5% by weight of the ABS part material, more preferablyfrom about 0.5% by weight to about 2% by weight, and even morepreferably from about 0.75% by weight to about 1.5% by weight, based onthe entire weight of the ABS part material. As discussed above, thesecharge control agents preferably increase the charging rate of the ABScopolymer against the carrier, and stabilize the Q/M ratio over extendedcontinuous periods of printing operations with system 10.

In many situations, system 10 prints layers 64 p with a substantiallyconsistent material density over the duration of the printingoperations. Having an ABS part material with a controlled and consistentQ/M ratio allows this to be achieved. However, in some situations, itmay be desirable to adjust the material density between the variouslayers 64 p in the same printing operation. For example, system 10 maybe operated to run in a grayscale manner with reduced material density,if desired, for one or more portions of 3D part 80.

In addition to incorporating the charge control agents, for efficientoperation EP engine 12 p, and to ensure fast and efficient triboelectriccharging during replenishment of the ABS part material, the mixture ofthe ABS part material preferably exhibits good powder flow properties.This is preferred because the ABS part material is fed into adevelopment sump (e.g., a hopper) of development station 58 by auger,gravity, or other similar mechanism, where the ABS part materialundergoes mixing and frictional contact charging with the carrierparticles.

As can be appreciated, blockage or flow restrictions of the ABS partmaterial during the replenishment feeding can inhibit the supply of theABS part material to the carrier particles. Similarly, portions of theABS part material should not become stuck in hidden cavities indevelopment station 58. Each of these situations can alter the ratio ofthe ABS part material to the carrier particles, which, as discussedabove, is preferably maintained at a constant level to provide thedesired Q/M ratio for the charged ABS part material.

For example, the ABS part material may constitute from about 1% byweight to about 30% by weight, based on a combined weight of the ABSpart material and the carrier particles, more preferably from about 5%to about 20%, and even more preferably from about 5% to about 10%. Thecarrier particles accordingly constitute the remainder of the combinedweight.

The powder flow properties of the ABS part material can be improved orotherwise modified with the use of one or more flow control agents, suchas inorganic oxides. Examples of suitable inorganic oxides includehydrophobic fumed inorganic oxides, such as fumed silica, fumed titania,fumed alumina, mixtures thereof, and the like, where the fumed oxidesmay be rendered hydrophobic by silane and/or siloxane-treatmentprocesses. Examples of commercially available inorganic oxides for usein the ABS part material include those under the tradename “AEROSIL”from Evonik Industries AG, Essen, Germany.

The flow control agents (e.g., inorganic oxides) preferably constitutefrom about 0.1% by weight to about 10% by weight of the ABS partmaterial, more preferably from about 0.2% by weight to about 5% byweight, and even more preferably from about 0.3% by weight to about 1.5%by weight, based on the entire weight of the ABS part material.

As discussed above, the one or more charge control agents are suitablefor charging the ABS copolymer to a desired Q/M ratio for developinglayers of the ABS part material at EP engine 12 p, and for transferringthe developed layers (e.g., layers 64) to layer transfusion assembly 20(e.g., via belt 22). However, the multiple printed layers in a 3Denvironment effectively prevents the electrostatic transfer of ABS partmaterial after a given number of layers are printed. Instead, layertransfusion assembly 20 utilizes heat and pressure to transfuse thedeveloped layers together in the transfusion steps.

In particular, heaters 72 and/or 74 may heat layers 64 and the topsurfaces of 3D part 80 and support structure 82 to a temperature near anintended transfer temperature of the ABS part material, such as at leasta fusion temperature of the ABS part material, prior to reaching niproller 70. Similarly, post-fuse heater 76 is located downstream from niproller 70 and upstream from air jets 78, and is configured to heat thetransfused layers to an elevated temperature in the post-fuse orheat-setting step.

Accordingly, the ABS part material may also include one or more heatabsorbers configured to increase the rate at which the ABS part materialis heated when exposed to heater 72, heater 74, and/or post-heater 76.For example, in embodiments in which heaters 72, 74, and 76 are infraredheaters, the heat absorber(s) used in the ABS part material may be oneor more infrared (including near-infrared) wavelength absorbingmaterials. As discussed below, these heat absorbers may be incorporatedinto the particles of the ABS copolymer during the manufacturing of theABS part material. Absorption of infrared light causes radiationlessdecay of energy to occur within the particles, which generates heat inthe ABS part material.

The heat absorber is preferably soluble or dispersible in the solvatedABS copolymers used for the preparation of the ABS part material with alimited coalescence process, as discussed below. Additionally, the heatabsorber also preferably does not interfere with the formation of theABS copolymer particles, or stabilization of these particles during themanufacturing process. Furthermore, the heat absorber preferably doesnot interfere with the control of the particle size and particle sizedistribution of the ABS copolymer particles, or the yield of the ABScopolymer particles during the manufacturing process.

Suitable infrared absorbing materials for use in the ABS part materialmay vary depending on the desired color of the ABS part material.Examples of suitable infrared absorbing materials include carbon black(which may also function as a black pigment for the ABS part material),as well as various classes of infrared absorbing pigments and dyes, suchas those that exhibit absorption in the wavelengths ranging from about650 nanometers (nm) to about 900 nm, those that exhibit absorption inthe wavelengths ranging from about 700 nm to about 1,050 nm, and thosethat exhibit absorption in the wavelengths ranging from about 800 nm toabout 1,200 nm. Examples of these pigments and dyes classes includeanthraquinone dyes, polycyanine dyes metal dithiolene dyes and pigments,tris aminium dyes, tetrakis aminium dyes, mixtures thereof, and thelike.

The infrared absorbing materials also preferably do not significantlyreinforce or otherwise alter the melt rheologies of the ABS copolymer,such as the zero shear viscosity versus temperature profile of the ABScopolymer. For example, this can be achieved using a non-reinforcingtype of carbon black, or a “low structure” type of carbon black, at lowconcentrations relative to the ABS copolymer. Accordingly, suitabledynamic viscosities for the ABS part material include those discussedabove for the ABS copolymer at 180° C., 190° C., and 200° C.

Accordingly, in embodiments that incorporate heat absorbers, the heatabsorbers (e.g., infrared absorbers) preferably constitute from about0.5% by weight to about 10% by weight of the ABS part material, morepreferably from about 1% by weight to about 5% by weight, and in somemore preferred embodiments, from about 2% by weight to about 3% byweight, based on the entire weight of the ABS part material.

The ABS part material may also include one or more additional additivesthat are preferably soluble or dispersible in the solvated ABScopolymers used for the preparation of the ABS part material with alimited coalescence process, that preferably do not interfere with theformation of the ABS copolymer particles, or stabilization of theseparticles during the manufacturing process, and that preferably do notinterfere with the control of the particle size and particle sizedistribution of the ABS copolymer particles, or the yield of the ABScopolymer particles during the manufacturing process.

Examples of suitable additional additives include colorants (e.g.,pigments and dyes in addition to, or alternatively to, the heatabsorbers), polymer stabilizers (e.g., antioxidants, light stabilizers,ultraviolet absorbers, and antiozonants), biodegradable additives, andcombinations thereof. In embodiments that incorporate additionaladditives, the additional additives may collectively constitute fromabout 0.1% by weight to about 20% by weight of the ABS part material,more preferably from about 0.2% by weight to about 10% by weight, andeven more preferably from about 0.5% by weight to about 5% by weight,based on the entire weight of the ABS part material.

For use in electrophotography-based additive manufacturing systems(e.g., system 10), the ABS part material preferably has a controlledaverage particle size and a narrow particle size distribution, asdescribed below in the Particle Sizes and Particle Size Distributionsstandard. For example, preferred D50 particles sizes include those up toabout 100 micrometers if desired, more preferably from about 10micrometers to about 30 micrometers, more preferably from about 10micrometers to about 20 micrometers, and even more preferably from about10 micrometers to about 15 micrometers.

Additionally, the particle size distributions, as specified by theparameters D90/D50 particle size distributions and D50/D10 particle sizedistributions, each preferably range from about 1.00 to 1.40, morepreferably from about 1.10 and to about 1.35, and even more preferablyfrom about 1.15 to about 1.25. Moreover, the particle size distributionis preferably set such that the geometric standard deviation σ_(g)preferably meets the criteria pursuant to the following Equation 1:

${\sigma \; g} \sim \frac{D\; 90}{D\; 50} \sim \frac{D\; 50}{D\; 10}$

In other words, the D90/D50 particle size distributions and D50/D10particle size distributions are preferably the same value or close tothe same value, such as within about 10% of each other, and morepreferably within about 5% of each other.

The ABS part material is preferably manufactured by polymerizing orotherwise providing the ABS copolymer, and then formulating the ABS partmaterial from the ABS copolymer (and other components) with theabove-discussed particle sizes and particle size distributions. The ABScopolymer exhibits good impact resistance and toughness. Unfortunately,these desirable engineering properties make it difficult to mechanicallygrind the copolymer down to a size useful for the electrophotographicdevelopment process in EP engine 12 p, particularly for theabove-discussed particle sizes and particle size distributions. In fact,traditional grinding and pulverization methods are typically onlycapable of obtaining particle sizes around 30-60 micrometers, and in alow yield and production cost-inefficient manner.

Various other manufacturing processes have been examined to solve thisproblem, such as cryogenic grinding and milling where the ABS copolymeris embrittled using liquid nitrogen, dry ice (solid carbon dioxide)followed by mechanical pulverization, and pregrinding of pelletsfollowed by air jet milling. Using these technologies may also provecost-ineffective if grinding rates are particularly slow.

Instead, the ABS part material is preferably formulated from the ABScopolymer with a limited coalescence process, such as the processdisclosed in Bennett et al., U.S. Pat. No. 5,354,799. For example, theconstituents of the ABS part material (e.g., the ABS copolymer andcharge control agent, heat absorber, and/or additional additives) may bedissolved or otherwise suspended in an organic solvent to a suitableconcentration range such as from about 10% to about 20% by weight of theABS copolymer in the organic solvent. Examples of suitable organicsolvents include ethyl acetate, propyl acetate, butyl acetate,dichloromethane, methyl ethyl ketone, cyclohexane, toluene, mixturesthereof, and the like.

Separately, a buffered acidic aqueous solution may be preparedcontaining a dispersant such as colloidal silica, and preferably awater-droplet interface promoter, such as poly(adipicacid-co-methylaminoethanol). The organic solvent solution may then beslowly (e.g., incrementally) added to the buffered acidic aqueoussolution while subjecting the whole mixture to high shear mixing, suchas with a homogenizer. This creates droplets of the organic phase ofcontrolled size and size distribution, which are stabilized by thecolloidal silica in the aqueous phase. This mixing preferably continuesuntil droplet growth and creation is completed.

The stabilized solvated droplet suspension may then be passed to a flashevaporator, where the organic solvent may be removed to a condensatetank using applied vacuum. The solid particles of the resulting ABS partmaterial, which remain dispersed in the aqueous phase, may then betransferred to a stirred holding vessel, and the colloidal silica may beremoved, such as with the use of an aqueous sodium hydroxide solution,filtration, and water.

The ABS part material may then be dried to produce its powder form. Ifnecessary, following particle size analysis, the dry powder of the ABSpart material may be subjected to further sieving to remove oversizeparticles, and/or classification to remove any level of fines that areconsidered detrimental to subsequent performance in system 10. Thisprocess typically produces the ABS part material in a yield ranging fromabout 90% by weight to about 99% by weight, based on the original amountof the ABS copolymer employed.

The ABS part material also has particle sizes and particle sizedistributions as discussed above. In some embodiments, the resulting ABSpart material may be surface treated with one or more external flowcontrol agents, as discussed above, to increase the powder flowproperties of the ABS part material. For example, the ABS part materialmay be dry blended in a high speed and high shear cyclonic mixingapparatus, preferably at 25° C., with one or more external flow controlagents. This uniformly distributes, coats, and partially embeds the flowcontrol agent(s) into the individual particles of the ABS part material,without significantly altering the particle size or particle sizedistribution.

The formulated ABS part material may then be filled into a cartridge orother suitable container for use with EP engine 12 p in system 10. Forexample, the formulated ABS part material may be supplied in acartridge, which may be interchangeably connected to a hopper ofdevelopment station 58. In this embodiment, the formulated ABS partmaterial may be filled into development station 58 for mixing with thecarrier particles, which may be retained in development station 58.Development station 58 may also include standard toner developmentcartridge components, such as a housing, delivery mechanism,communication circuit, and the like.

The carrier particles in development station 58 may be any suitablemagnetizable carrier particles for charging the ABS part material, suchas carrier particles having strontium ferrite cores with polymercoatings. The cores are typically larger in size than the particles ofthe ABS part material, such as averaging from about 20 micrometers toabout 25 micrometers in diameter. The polymer coatings may varydepending on the Q/M ratios desired for the ABS part material. Examplesof suitable polymer coatings include poly(methyl methacrylate) (PMMA)for negative charging, or poly(vinylidene fluoride) (PVDF) for positivecharging. Suitable weight ratios of the ABS part material to the carrierparticles in development station or cartridge 58 include those discussedabove.

Alternatively, development station 58 itself may be an interchangeablecartridge device that retains the supply of the ABS part material. Infurther alternative embodiments, EP engine 12 p itself may be aninterchangeable device that retains the supply of the ABS part material.

When the ABS part material is loaded to system 10, system 10 may thenperform printing operations with the ABS part material to print 3D parts(e.g., 3D part 80), preferably with a suitable support structure (e.g.,support structure 82). For instance, the layers 64 s of supportstructure 82 may be developed from the support material 66 s with EPengine 12 s and transferred to layer transfusion assembly 20 along withlayers 64 p of the developed part material 66 p, via belt 22. Uponreaching layer transfusion assembly the combined layer 64 (of layers 64p and 64 s) are heated and transfused to print 3D part 80 and supportstructure 82 in a layer-by-layer manner using an additive manufacturingtechnique.

Compositionally, the resulting 3D part (e.g., 3D part 80) includes theABS part material, such as the ABS copolymer, charge control agent, heatabsorber, flow control agent, and/or any additional additives.Furthermore, the transfusion steps with layer transfusion assembly 20may provide part densities that are greater than those achievable fromABS copolymers with other fusion-based additive manufacturingtechniques, such as the extrusion-based technique developed byStratasys, Inc., Eden Prairie, Minn., under the trademarks “FUSEDDEPOSITION MODELING” and “FDM”.

For example, in a direction of the build plane, the resulting 3D partmay exhibit a peak tensile stress greater than about 5,000pounds/square-inch (psi), and more preferably greater than about 5,300psi. In some embodiments, the 3D part may exhibit a peak tensile stressgreater than about 5,800 psi in a direction of the build plane. As usedherein, the peak tensile stress is measured pursuant to ASTM D638-10.Accordingly, the printed 3D parts may have high part resolutions andgood physical properties (e.g., good part strength, density, chemicalresistance, usable temperature ranges, and the like), allowing them tofunction as end-use parts, if desired.

Property Analysis and Characterization Procedures

Various properties and characteristics of the part and support materialsdescribed herein may be evaluated by various testing procedures asdescribed below:

1. Glass Transition Temperature

The glass transition temperature is determined using the classical ASTMmethod employing Differential Scanning Calorimetry (DSC) ASTM D3418-12e1and is reported in degrees Celsius. The test is performed with a DSCanalyzer commercially available under the tradename “SEIKO EXSTAR 6000”from Seiko Instruments, Inc., Tokyo, Japan, with a 10-milligram sampleof the support material copolymer. The data is analyzed using softwarecommercially available under the tradenames “DSC Measurement V 5.7” and“DSC Analysis V5.5”, also from Seiko Instruments, Inc., Tokyo, Japan.The temperature profile for the test includes (i) 25° C. to 160° C.heating rate 10 Kelvin/minute (first heating period), (ii) 160° C. to20° C. cooling rate 10 Kelvin/minute, and (iii) 20° C. to 260° C.heating rate 10 Kelvin/minute (second heating period). The glasstransition temperature is determined using only the heat flowcharacteristics of the second heating period (iii).

2. Particle Size and Particle Size Distribution

Particle sizes and particle size distributions are measured using aparticle size analyzer commercially available under the tradename“COULTER MULTISIZER II ANALYZER” from Beckman Coulter, Inc., Brea,Calif. The particle sizes are measured on a volumetric-basis based onthe D50 particles size, D10 particle size, and D90 particles sizeparameters. For example, a D50 particle size of 10.0 micrometers for asample of particles means that 50% of the particles in the sample arelarger than 10.0 micrometers, and 50% of the particles in the sample aresmaller than 10.0 micrometers. Similarly, a D10 particle size of 9.0micrometers for a sample of particles means that 10% of the particles inthe sample are smaller than 9.0 micrometers. Moreover, a D90 particlesize of 12.0 micrometers for a sample of particles means that 90% of theparticles in the sample are smaller than 12.0 micrometers.

Particle size distributions are determined based on the D90/D50distributions and the D50/D10 distributions. For example, a D50 particlesize of 10.0 micrometers, a D10 particle size of 9.0 micrometers, and aD90 particle size of 12.0 micrometers provides a D90/D50 distribution of1.2, and a D50/D10 distribution of 1.1.

As mentioned above, the geometric standard deviation σ_(g) preferablymeets the criteria pursuant to the above-shown Equation 1, where theD90/D50 distributions and D50/D10 distributions are preferably the samevalue or close to the same value. The “closeness of the D90/D50distributions and D50/D10 distributions are determined by the ratio ofthe distributions. For example, a D90/D50 distribution of 1.2 and aD50/D10 distribution of 1.1 provides a ratio of 1.2/1.1=1.09, or about a9% difference.

3. Triboelectric Charging

The triboelectric or electrostatic charging properties of powder-basedmaterials for use in electrophotography-based additive manufacturingsystems, such as system 10, may be determined with the followingtechnique. A test sample of 7 parts by weight of the powder-basedmaterial is agitated in a clean dry glass bottle with 93 parts by weightof carrier particles. The carrier particles include a magnetized22-micrometer core of strontium ferrite coated with 1.25% by weight of apolymer coating of poly(methyl methacrylate) (PMMA) for negativecharging, or poly(vinylidene fluoride) (PVDF) for positive charging.

The mixture of the powder-based material and the carrier particles isagitated 25° C. on a jar roller for 45 minutes to ensure complete mixingof the carrier particles and the powder-based material, and to ensureequilibration of the Q/M ratios. This mixing simulates the mixingprocess that occurs in a development station of the electrophotographyengine when the part or support materials are added to the carrierparticles.

A sample of the mixture is then quantitatively analyzed with a TEC-3Triboelectric Charge Analyzer (available from Torrey Pines Research,Fairport, N.Y.). This analyzer uses electric fields to strip theelectrostatic powder from the carrier particle surface, and a rotatinghigh-strength, planar multi-pole magnet to constrain the (magnetizableor permanently magnetized) carrier beads to a bottom electrode.

A 0.7-gram sample of the mixture (sample powder and carrier particles)is placed onto a clean stainless steel disc, which serves as the bottomelectrode in an electrostatic plate-out experiment across a gap, underthe influence of an applied electric field. This bottom electrode ismounted and positioned above the rotating multi-pole magnet, and a cleantop plate disc electrode is mounted securely above the bottom plate, andparallel to it, so as to provide a controlled gap of 5 millimetersbetween the top and bottom electrode plates, using insulatingpolytetrafluoroethylene (PTFE under tradename “TEFLON”) spacers at theelectrodes' periphery.

If the powder is expected to charge negatively, a direct-current voltageof +1,500 volts is applied across the electrodes, and the magneticstirrer is activated to rotate at 1500 rpm, so as to gently keep thecarrier and powder under test constrained, but also slightly agitated onthe bottom electrode, during the measurement. Alternatively, if thepowder is expected to charge positively, then a negative bias voltage of−1,500 volts is applied. In either case, the applied electric fieldcauses the powder to strip from the carrier, in the powder/carriermixture, and to transfer to the top electrode, over a defined timeperiod.

The stripped powder under test is deposited on the top electrode, andthe induced accumulated charge on the top plate is measured using anelectrometer. The amount of powder transferred to the top electrode isweighed, and compared to the theoretical percentage in the originalcarrier powder mix. The carrier remains on the bottom plate due to themagnetic forces constraining it.

The total charge on the top plate and the known weight of transferredelectrostatic powder are used to calculate the Q/M ratio of the testpowder, and to also check that all the electrostatic powder hastransferred from the carrier, according to the theoretical amountoriginally mixed with the carrier beads. The time taken for completepowder transfer to the top plate, and the percent efficiency of thepowder transfer process are also measured.

4. Powder Flowability

As discussed above, the part and support materials of the presentdisclosure preferably exhibit good powder flow properties. This reducesor prevents blockage or flow restrictions of the part or supportmaterial during the replenishment feeding, which can otherwise inhibitthe supply of the part or support material to the carrier particles inthe development station. The powder flowability of a sample material isqualitatively measured by visually observing the flowability of thepowder in comparison to commercially-available toners utilized intwo-dimensional electrophotography processes, which are rated as having“good flow” or “very good flow”.

5. Melt Rheology

Preferably, the melt rheologies of the part and support materials aresubstantially the same as the melt rheologies of their respectivecopolymers, and are preferably not detrimentally affected by the otheradditives. Additionally, as discussed above, the part and supportmaterials for use with electrophotography-based additive manufacturingsystems (e.g., system 10) preferably have similar melt rheologies.

Melt rheologies of the part and support materials of the presentdisclosure, and their respective copolymers, are measured based on theirmelt flow indices over a range of temperatures. The melt flow indicesare measured using a rheometer commercially available under thetradename “SHIMADZU CFT-500D” Flowtester Capillary Rheometer fromShimadzu Corporation, Tokyo, Japan. During each test, a 2-gram sample isloaded to the rheometer pursuant to standard operation of the rheometer,and the temperature of the sample is increased to 50° C. to cause aslight compacting of the sample.

The temperature is then increased from 50° C. at a rate of 5° C. perminute, allowing the sample to first soften and then flow. The rheometermeasures the sample viscosity using the flow resistance of the melt toflow through a small die orifice, as a piston of the rheometer is driventhrough a cylinder. The rheometer records the softening point, thetemperature at which flow begins, and the rate at which flow increasesas a result of the temperature increase, until the cylinder is exhaustedof sample melt. The rheometer also calculates the apparent viscosity inPascal-seconds at each temperature point in the ramp. From this data,the apparent viscosity versus temperature profile can be determined,such as shown in FIG. 5, for example.

EXAMPLES

The present disclosure is more particularly described in the followingexamples that are intended as illustrations only, since numerousmodifications and variations within the scope of the present disclosurewill be apparent to those skilled in the art.

1. Example 1

An ABS part material of Example 1 was produced using a limitedcoalescence process, which included an ABS copolymer, but did notinclude any charge control agent, flow control agent, or infraredabsorber. The ABS copolymer was dissolved in an organic solvent (ethylacetate) to a concentration of 15% by weight.

Separately, a buffered acidic aqueous solution was prepared containingcolloidal silica and poly(adipic acid-co-methylaminoethanol. The pH wasadjusted to pH 4.0 using dilute hydrochloric acid. The solvent solutionwas then added slowly to the buffered acidic aqueous solution whilesubjecting the whole mixture to high shear mixing with a homogenizer.This created droplets of the organic phase of controlled size and sizedistribution, which were stabilized by the colloidal silica in theaqueous phase.

The organic phase droplet size was targeted to deliver a final size ofthe dry ABS part material of 11 micrometers. The stabilized solvateddroplet suspension was then passed to a flash evaporator, where theorganic solvent was removed to a condensate tank using applied vacuum.

The solid particles of the resulting ABS part material, which remaineddispersed in the aqueous phase, were then transferred to a stirredholding vessel. A 0.1% sodium hydroxide solution was then added toremove the colloidal silica. The resulting aqueous slurry was thenpumped through a particle filtration device and washed on the filterwith 0.1% sodium hydroxide, followed by demineralized water, to removeany remaining colloidal silica particles.

The resultant colorless ABS part material, which did not include anycharge control agent, flow control agent, or infrared absorber, was thendried using hot air in a tray drying apparatus, which produced a 94%yield relative to the original amount of the ABS copolymer, and aparticle size and particle size distribution as listed below in Table 1.

TABLE 1 Particle Size/Particle Size Distribution Example 1 D50 ParticleSize (micrometers) 10.42 D90 Particle Size (micrometers) 13.02 D10Particle Size (micrometers) 8.92 D90/D50 Distribution 1.25 D50/D10Distribution 1.14

2. Example 2

An ABS part material of Example 2 was produced using the same limitedcoalescence process as discussed above for Example 1 where the ABS partmaterial of Example 2 included a charge control agent (zinc complex ofdi-t-butyl salicylate) in addition to the ABS copolymer, but did notinclude any flow control agent or infrared absorber. The limitedcoalescence process followed the same steps as discussed above forExample 1, where the charge control agent was also added to the organicsolvent with the ABS copolymer.

The resulting powder of the ABS part material included the ABS copolymerand 1% by weight of the charge control agent. This produced a 93% yieldrelative to the original amount of the ABS copolymer, and a particlesize and particle size distribution as listed below in Table 2.

TABLE 2 Particle Size/Particle Size Distribution Example 2 D50 ParticleSize (micrometers) 11.69 D90 Particle Size (micrometers) 13.95 D10Particle Size (micrometers) 9.66 D90/D50 Distribution 1.19 D50/D10Distribution 1.21

3. Example 3

An ABS part material of Example 3 was produced using the same limitedcoalescence process as discussed above for Example 1 where the ABS partmaterial of Example 3 included another charge control agent (chromiumcomplex of di-t-butyl salicylate) in addition to the ABS copolymer, butdid not include any flow control agent or infrared absorber. The limitedcoalescence process followed the same steps as discussed above forExample 1, where the charge control agent was also added to the organicsolvent with the ABS copolymer.

The resulting powder of the ABS part material included the ABS copolymerand 1% by weight of the charge control agent. This produced a 93% yieldrelative to the original amount of the ABS copolymer, and a particlesize and particle size distribution as listed below in Table 3.

TABLE 3 Particle Size/Particle Size Distribution Example 3 D50 ParticleSize (micrometers) 11.49 D90 Particle Size (micrometers) 13.77 D10Particle Size (micrometers) 9.46 D90/D50 Distribution 1.20 D50/D10Distribution 1.21

4. Example 4

An ABS part material of Example 4 was produced using the same limitedcoalescence process as discussed above for Example 1 where the ABS partmaterial of Example 4 included the charge control agent of Example 2(zinc complex of di-t-butyl salicylate) and carbon black infraredabsorber, in addition to the ABS copolymer, but did not include any flowcontrol agent.

The limited coalescence process followed the same steps as discussedabove for Example 1, where the charge control agent and the carbon blackwere also added to the organic solvent with the ABS copolymer. Inparticular, the carbon black was commercially available under thetradename “REGAL 330” from Cabot Corporation, Boston, Mass., and waspassed through a microfluidizer for dispersion into the organic solventsolution. Additionally, the organic phase droplet size was targeted todeliver a final size of the dry ABS part material of 12 micrometers.

The resulting powder of the ABS part material included the ABScopolymer, 1% by weight of the charge control agent, and 2.5% by weightof the carbon black. This produced a 97% yield relative to the originalamount of the ABS copolymer, and a particle size and particle sizedistribution as listed below in Table 4.

TABLE 4 Particle Size/Particle Size Distribution Example 4 D50 ParticleSize (micrometers) 12.09 D90 Particle Size (micrometers) 14.38 D10Particle Size (micrometers) 10.00 D90/D50 Distribution 1.19 D50/D10Distribution 1.21

5. Example 5

The ABS part material of Example 4 was further subjected to sievingthrough a 300-micrometer mesh and classification using a classifieroperating at 13,000 rpm, where the classifier was commercially availablefrom Hosokawa Micron Ltd., Cheshire, England. After sieving andclassification, the resulting yield was 92% relative to the originalamount of the ABS part material subjected to the sieving andclassification. The resulting particle size and particle sizedistribution as listed below in Table 5.

TABLE 5 Particle Size/Particle Size Distribution Example 5 D50 ParticleSize (micrometers) 12.11 D90 Particle Size (micrometers) 14.20 D10Particle Size (micrometers) 10.23 D90/D50 Distribution 1.18 D50/D10Distribution 1.18

The resulting ABS part material was then surface treated with a flowcontrol agent, which was a dimethyldichlorosilane-treated fumed silicacommercially available under the tradename “AEROSIL R972” from EvonikIndustries AG, Essen, Germany. This produced an ABS part material ofExample 5 having the ABS copolymer, 1% by weight of the charge controlagent, 0.5% by weight of the flow control agent, and 2.5% by weight ofthe carbon black.

6. Example 6

An ABS part material of Example 6 was produced using the same limitedcoalescence process as discussed above for Example 1 where the ABS partmaterial of Example 6 included the carbon black infrared absorber ofExample 4, in addition to the ABS copolymer, but did not include anycharge control agent or flow control agent. The organic phase dropletsize was targeted to deliver a final size of the dry ABS part materialof 11 micrometers.

The resulting powder of the ABS part material included the ABS copolymerand 2.5% by weight of the carbon black. This produced a 96% yieldrelative to the original amount of the ABS copolymer, and a particlesize and particle size distribution as listed below in Table 6.

TABLE 6 Particle Size/Particle Size Distribution Example 6 D50 ParticleSize (micrometers) 10.52 D90 Particle Size (micrometers) 12.68 D10Particle Size (micrometers) 8.81 D90/D50 Distribution 1.21 D50/D10Distribution 1.19

7. Example 7

An ABS part material of Example 7 was produced using the same limitedcoalescence process as discussed above for Example 1 where the ABS partmaterial of Example 7 included the carbon black infrared absorber ofExample 4, in addition to the ABS copolymer, but did not include anycharge control agent or flow control agent. In this example, the carbonblack concentration was doubled compared to that of Example 6. Theorganic phase droplet size was targeted to deliver a final size of thedry ABS part material of 12 micrometers.

The resulting powder of the ABS part material included the ABS copolymerand 2.5% by weight of the carbon black. This produced a 93% yieldrelative to the original amount of the ABS copolymer, and a particlesize and particle size distribution as listed below in Table 7.

TABLE 7 Particle Size/Particle Size Distribution Example 7 D50 ParticleSize (micrometers) 10.18 D90 Particle Size (micrometers) 12.30 D10Particle Size (micrometers) 8.51 D90/D50 Distribution 1.21 D50/D10Distribution 1.20

As shown above in Tables 1-7, the limited coalescence processes used toproduce the ABS part materials of Examples 1-7 provided good control ofthe particle size and particle size distributions, and were largelyindependent of changes in ABS powder formulation. The particle sizemedians were within about 0.5 micrometers of the targeted values, andthe particle size distributions were within targeted specifications interms of D90/D50 and D50/D10 distributions. Table 8 shown below providesa summary of the formulations for the part materials of Examples 1-7,where the values are weight percent based.

TABLE 8 ABS Charge Control Flow Control Example Copolymer Agent AgentCarbon Black Example 1 100.0 0.0 0.0 0.0 Example 2 99.0 1.0 0.0 0.0Example 3 99.0 1.0 0.0 0.0 Example 4 96.5 1.0 0.0 2.5 Example 5 96.0 1.00.5 2.5 Example 6 97.5 0.0 0.0 2.5 Example 7 95.0 0.0 0.0 5.0

8. Triboelectric Charging Testing for Examples 1-7

The ABS part materials of Examples 1-7 were subjected to triboelectriccharging analysis pursuant to the Triboelectric Charging test describedabove. Each sample was tested with carrier particles having PMMAcoatings, which provided negative charges. Additionally, the sample ofExample 1 was also tested with carrier particles having PVDF coatings,which provided positive charges. Table 9 lists the results of thetriboelectric charging tests for the ABS part materials of Examples 1-7.

TABLE 9 Carrier Particles Q/M Ratio Transit Time Transit Example Coating(μC/g) (seconds) Efficiency Example 1 PMMA −28 ± 1 >360 90% Example 1PVDF +24 ± 1 >300 95% Example 2 PMMA −22 ± 1 120 95% Example 3 PMMA −25± 1 120 95% Example 4 PMMA −18 ± 1 45 98% Example 5 PMMA −27 ± 1 30 100%Example 6 PMMA −12 ± 1 60 94% Example 7 PMMA  −9 ± 1 60 96%

As shown in Table 9, the Q/M ratios of the ABS part materials aredependent on the types of carrier particles used. Furthermore, thefastest transit times and greatest powder transit efficiencies wereachieved using a combination of a charge control agent and carbon blackas internal additives, and the flow control agent as a powder flowsurface additive (i.e., Example 5).

Moreover, the long term stability of the Q/M ratio and the powderflowability was investigated by exercising the mixture for several hoursin a powder development station (e.g., development station 58). As alsoshown in Table 9, the greatest stability of both the Q/M ratio and thepowder flowability was exhibited by the ABS part material of Example 5.

9. Powder Flowability Testing for Examples 1-7

The ABS part materials of Examples 1-7 were also qualitatively measuredfor powder flowability pursuant to the Powder Flowability test describedabove. Table 10 lists the results of the powder flowability tests forthe ABS part materials of Examples 1-7.

TABLE 10 Example Powder Flow Results Example 1 Very poor flow Example 2Poor flow Example 3 Poor flow Example 4 Good flow Example 5 Very goodflow Example 6 Moderate flow Example 7 Moderate flow

As shown in Table 10, the ABS part materials of Examples 4-7, whichincorporated carbon black, exhibited suitable levels of powderflowability. Particularly, the ABS part material of Example 4 (1% chargecontrol agent and 2.5% carbon black) exhibited good flowability, and theABS part material of Example 5 (1% charge control agent, 0.5% flowcontrol agent, and 2.5% carbon black) exhibit very good flowability.

Thus, the incorporation of the carbon black and the charge controlagent, and more importantly, the flow control agent, may combine toincrease the powder flowability of the ABS part materials. As discussedabove, this reduces or prevents blockage or flow restrictions of the ABSpart material during the replenishment feeding, which can otherwiseinhibit the supply of the ABS part material to the carrier particles inthe development station.

10. Melt Rheology Testing for Examples 1, 4, 6, and 7

The ABS part materials of Examples 1, 4, 6, and 7 were also testedpursuant to the Melt Rheology test described above to determine whetherthe additives, such as the charge control agents and the carbon black,had any detrimental effects on the melt rheologies of the ABS copolymer.FIG. 5 is a plot of the resulting dynamic viscosities versus temperaturefor the tests, where the results of the ABS copolymer feedstock was alsotested for comparison.

As shown in FIG. 5, the incorporation of the charge control agent (1% byweight) and the carbon black (2.5% by weight and 5.0% by weight) did nothave any significant detrimental effects on the melt rheology of the ABScopolymer. As such, the inclusion of the charge control agent and thecarbon black at concentrations shown to be effective for use inelectrophotography-based additive manufacturing systems allow theresulting ABS part materials to have melt rheology behaviors that aresubstantially the same as the ABS copolymer feedstock.

11. Printing Runs for Example 5

The ABS part material of Example 5 was also used to print multiple 3Dparts of different geometries, with and without an associated supportmaterial, with an electrophotography-based additive manufacturing systemcorresponding to system 10 (without heater 74). In printing runs with asupport material, the support material included a thermoplasticcopolymer of styrene-butyl acrylate-methacrylic acid, 2.5% by weight ofthe carbon black heat absorber, and 1% by weight of the charge controlagent, 2.5% by weight of the carbon black heat absorber, and 0.5% byweight of the flow control agent, as described in Example 16 of co-filedU.S. patent application Ser. No. ______, entitled “Soluble SupportMaterial For Electrophotography-Based Additive Manufacturing” (attorneydocket no. S697.12-0261).

During a given printing run, a digital model of a 3D part was slicedinto multiple layers, and support layers were then generated to supportoverhanging regions of the 3D part. Printing information for the slicedlayers was then transmitted to the electrophotography-based additivemanufacturing system, which was then operated to print the 3D part.

During the printing run, the ABS part material and the support materialwere each charged and developed in multiple successive layers with an EPengine of the system, where the development drums was each charged at−500 volts. The charge control agents and the flow control agents weresufficient to develop the layers with good material density. Thedeveloped layers were then transferred to an intermediary drums chargedat +450 volts, and were then transferred to a transfer belt of thesystem with biasing rollers charged at +2,000 volts. The part andsupport material layers were then transferred together to the layertransfusion assembly of the system, where the Q/M ratios of the part andsupport materials were also sufficient to maintain electrostaticattraction of the developed layers to the belt.

At the pre-heater (corresponding to heater 72), each layer was heated byinfrared radiation to temperatures ranging from about 180° C. to about200° C. The heated layers were then pressed between the nip roller andthe reciprocating build platen (with the previously-printed layers ofthe 3D part), where the nip roller was maintained at a temperature of200° C., and an average nip pressure of about 40 pounds/square-inch(psi). Each layer successfully transferred from the belt and remainedadhered to the top surface of the 3D part/support structure. Afterpassing the nip roller, the top surface of the 3D part/support structurewas then heated with a post-heater (corresponding to post-heater 76) tofurther transfuse the layers, and then cooled down with air jets. Thisprocess was then repeated for each layer of the 3D part/supportstructure.

After the printing run was completed, the 3D part/support structure wasremoved from the system and exhibited good part resolutions upon visualinspection. The 3D part/support structure was then placed in a supportremoval system commercially available under the tradename “WAVEWASH”from Stratasys, Inc., Eden Prairie, Minn. The support removal systemsubjected the combined 3D part/support structure to an aqueous alkalinesolution under agitation for a standard operating duration. Uponcompletion, the support structure (from the support material of Example16) was dissolved away from the 3D part of the ABS part material.

Accordingly, the electrophotography-based additive manufacturing systemsuccessfully printed 3D parts and support structures from the ABS partmaterial of Example 5 and the support material. This is believed to bedue in part to the nearly identical melt viscosity versus temperatureprofiles, nearly identical glass transition temperatures, and nearlyidentical triboelectric charging properties of the part and supportmaterials. Furthermore, the layers were developed and transfused at fastprinting rates, with good adhesion, allowing the 3D parts and supportstructures to be printed with short printing durations and thin layers.

Additional 3D parts printed from the ABS part material of Example 5 werealso tested for peak stresses to determine their resistance to tensileloads in the build plane. Table 11 lists the peak stresses for fourdifferent samples of the ABS part material of Example 5, referred to asExamples 5A-5D.

TABLE 11 Peak Stress Peak Stress Example (pounds/square-inch)(megapascals) Example 5A 6469 44.6 Example 5B 5437 37.5 Example 5C 553438.1 Example 5D 6048 41.7

As shown in Table 11, the ABS part material of Example 5 successfullyprinted 3D parts having good resistance to tensile loads in the buildplane. This is believed to be due to the achievable material densitiesand good transfusion between the successive layers. Moreover, the goodtransfusion is believed to be due in part to the inclusion of the 2.5%by weight loading of the carbon black infrared absorber, which allowedthe ABS part material to be quickly heated with the heaters to transfusethe layers together.

Although the present disclosure has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the disclosure.

1. A part material for printing three-dimensional parts with anelectrophotography-based additive manufacturing system, the partmaterial comprising: a composition comprising: a copolymer comprisingacrylonitrile units, butadiene units, and aromatic units; a chargecontrol agent; and a heat absorber; wherein the part material isprovided in a powder form having a D50 particle size ranging from about5 micrometers to about 30 micrometers; and wherein the part material isconfigured for use in the electrophotography-based additivemanufacturing system having a layer transfusion assembly for printingthe three-dimensional parts in a layer-by-layer manner.
 2. The partmaterial of claim 1, wherein the aromatic units comprise styrene units.3. The part material of claim 2, wherein the copolymer comprises anacrylonitrile-butadiene-styrene (ABS) copolymer.
 4. The part material ofclaim 1, wherein the D50 particle size ranges from about 10 micrometersto about 20 micrometers.
 5. The part material of claim 1, wherein thepowder form also has a D90/D50 particle size distribution and a D50/D10particle size distribution each ranging from about 1.00 to about 1.40.6. The part material of claim 1, wherein the charge control agent isselected from the group consisting of chromium oxy carboxylic acidcomplexes, zinc oxy carboxylic acid complexes, aluminum oxy carboxylicacid complexes, and mixtures thereof.
 7. The part material of claim 1,wherein the charge control agent constitutes from about 0.1% by weightto about 5% by weight of the part material.
 8. The part material ofclaim 1, wherein the heat absorber constitutes from about 0.5% by weightto about 10% by weight of the part material.
 9. The part material ofclaim 1, and further comprising a flow control agent constituting fromabout 0.1% by weight to about 10% by weight of the part material.
 10. Apart material for printing three-dimensional parts with anelectrophotography-based additive manufacturing system, the partmaterial comprising: a composition comprising: anacrylonitrile-butadiene-styrene (ABS) copolymer; a charge control agentconstituting from about 0.1% by weight to about 5% by weight of the partmaterial; a flow control agent constituting from about 0.1% by weight toabout 10% by weight of the part material; and a heat absorberconstituting from about 0.5% by weight to about 10% by weight of thepart material; wherein the part material is provided in a powder formhaving a D50 particle size ranging from about 5 micrometers to about 30micrometers, and D90/D50 particle size distribution and a D50/D10particle size distribution each ranging from about 1.00 to about 1.40;and wherein the part material is configured for use in theelectrophotography-based additive manufacturing system having a layertransfusion assembly for printing the three-dimensional parts in alayer-by-layer manner.
 11. The part material of claim 10, wherein thepart material is formulated, at least in part, with a limitedcoalescence process.
 12. The part material of claim 10, wherein the D50particle size ranges from about 10 micrometers to about 20 micrometers.13. The part material of claim 10, wherein the ABS copolymer has a glasstransition temperature ranging from about 100° C. to about 115° C. 14.The part material of claim 10, wherein the charge control agent isselected from the group consisting of chromium oxy carboxylic acidcomplexes, zinc oxy carboxylic acid complexes, aluminum oxy carboxylicacid complexes, and mixtures thereof.
 15. A method for printing athree-dimensional part with an electrophotography-based additivemanufacturing system having an electrophotography engine, a transfermedium, and a layer transfusion assembly, the method comprising:providing a part material to the electrophotography-based additivemanufacturing system, the part material compositionally comprising acharge control agent, a heat absorber, and a copolymer havingacrylonitrile units, butadiene units, and aromatic units, and has apowder form; triboelectrically charging the part material to a Q/M ratiohaving a negative charge or a positive charge, and a magnitude rangingfrom about 5 micro-Coulombs/gram to about 50 micro-Coulombs/gram;developing layers of the three-dimensional part from the charged partmaterial with the electrophotography engine; electrostaticallyattracting the developed layers from the electrophotography engine tothe transfer medium; moving the attracted layers to the layertransfusion assembly with the transfer medium; and transfusing the movedlayers to previously-printed layers of the three-dimensional part withthe layer transfusion assembly.
 16. The method of claim 15, wherein thecopolymer comprises an acrylonitrile-butadiene-styrene (ABS) copolymer.17. The method of claim 15, wherein the ABS copolymer has a glasstransition temperature ranging from about 100° C. to about 115° C. 18.The method of claim 15, wherein the powder form of the part material hasa D50 particle size ranging from about 5 micrometers to about 30micrometers, and a D90/D50 particle size distribution and a D50/D10particle size distribution each ranging from about 1.00 to about 1.40.19. The method of claim 15, wherein the charge control agent constitutesfrom about 0.1% by weight to about 5% by weight of the part material,and wherein the heat absorber constitutes from about 0.5% by weight toabout 10% by weight of the part material.
 20. The method of claim 15,wherein the part material further comprises a flow control agentconstituting from about 0.1% by weight to about 10% by weight of thepart material.